Device for controlled lowering of mass load

ABSTRACT

Device consists of a linear actuator having a direction sensitive clutch engageable with a load-energized friction bearing surface during movement in the load-aiding direction for eliminating back driving by the load with no decrease in the forward efficiency of the device. Bi-directional braking may also be provided for preventing back driving of the actuator in either direction.

[ June 12, 1973 United States Patent [191 Geyer DEVICE FOR CONTROLLEDLOWERING 2,969,222 1/1967 192/8 R 0F MASS LOAD [75] Inventor: Howard M.Geyer, Dayton, Ohio Primary Examiner charles Myhre AssistantExaminerRandall Heald [73] Assignee: Pneumo Dynamics Corporation,Attorney stephen Mihaly Cleveland, Ohio Apr. 26, 1971 ABSTRACT [22]Filed:

[21] PP .2 13 8 Device consists of a linear actuator having a directionsensitive clutch engageable with a load-energized fric- 40 Ma 27 w R 1M5Rl F 7 U .R In 2 9 "M 1 R W 8 m" 2 u. 9 n. 1 mmh c n m m e u S n ll C s.t n Umh References Cited UNITED STATES PATENTS preventing back drivingof the actuator in either direction.

2,424,912 7/1947 Briggs et a1. 192/8 R 10 Claims, 4 Drawing FiguresPAIENTED 2373 HOWARD M. GEYER ATTORNEYS DEVICE FOR CONTROLLED LOWERINGOF MASS LOAD This invention relates generally as indicated to a devicefor controlled lowering of mass loads, and more particularly to a linearactuator device such as may be used as a cowling door actuator for jetengines and the like.

Linear actuators which require moderate to high mechanical efficiencyduring movement in opposition to the applied load oftentimes employ ballscrews or high lead acme screws for converting a rotary input drivemotion into translating or linear movement of the load. The primaryobjection to the use of such screws is that they are subject to backdriving by the load, whereby undesirable loss of position control of theload may occur during movement in the load-aiding direction.

The subject invention relates to certain improve.- ments in such linearactuator devices for preventing undesirable back driving or overhaulingof the applied load without loss of efficiency during movement againstthe opposing load, which is a principal object of the subject invention.

Another object is to provide such an actuator device which prevents backdriving by overhauling load applications in one or both directions.

A further object is to provide such an actuator device which requires anet positive input torque to be applied to move the actuator in theload-aiding direction.

These and other objects of the present invention may be achieved byproviding an actuator with a direction sensitive clutch which engages aload-energized friction bearing surface when the resultant external loadacting on the actuator is in the load overhauling or aiding directionfor absorbing the energy of the load tending to move the actuator in theback driving or overhauling direction. The energy absorption capabilityof the friction bearing surface is directly proportional to the appliedload, whereby loss of position control may be prevented in theload-aiding direction by requiring a net positive input torque to beapplied to the screw shaft to move the actuator in the load-aidingdirection.

During movement of the actuator against the applied load, thedirectional clutch disengages the friction bearing surface for highefficiency operation in the load opposing direction. Bi-directionalbraking may also be provided so that mass load or overhauling loadapplications requiring over-center motion may be prevented from backdriving the actuator in either direction.

To the accomplishment of the foregoing and related ends, the invention,then, comprises the features hereinafter fully described andparticularly pointed out in the claims, the following description andthe annexed drawings setting forth in detail certain illustrativeembodiments of the invention, these being indicative, however, of but afew of the various ways in which the principles of the invention may beemployed.

In the annexed drawings:

FIG. 1 is a fragmentary longitudinal section through a preferred form oflinear actuator device in accordance with this invention;

FIG. 2 is a transverse section through the linear actuator device ofFIG. 1, taken on the plane of the line 2-2 thereof;

FIG. 3 is a fragmentary longitudinal section through a modified form ofactuator device in accordance with this invention; and

FIG. 4 is a fragmentary longitudinal section through still another formof actuator device in accordance with this invention.

Referring now in detail to the drawings and first especially to FIG. 1,there is shown a linear actuator 1 in accordance with this inventionincluding a housing 2 having a tubular sleeve 3 projecting from one end4 thereof. Attached to the outer end of the tubular sleeve 3 is a'ballmount 5 received in a socket 6 of a mounting bracket 7 for providing aswivel connection for the actuator 1 when fastened to a stationarysupport. Contained within the-tubular sleeve 3 and housing 2 is a screwshaft 8, which may either be a ball screw type or high lead acme screwtype, having one end projecting outwardly from the other end 9 of thehousing and having a clevis mount 10 on the projecting end of the screwfor attachment to a load which prevents rotation of the screw.

Also contained within the housing 2 is a ball nut 11 having threadedengagement with the screw shaft 8.

The nut 11 may be spur gear driven by rotation of an input shaft 12having a spur gear 13 on the inner end thereof in meshing engagementwith a spur gear 14 on one end of the nut thus to cause linear movementof the screw shaft 8 relative to the nut 11 and housing 2. Attached tothe other end of the nut 11 is a one-way direction sensitive clutch 15which as more clearly shown in FIG. 2 may comprise a plurality of clutchrollers 16 contained in cam slots 17 in the outer periphery of acylindrical clutch element 18. Surrounding the cylindrical clutchelement 18 is a sleeve 19 rotatably received in a bushing 20 adjacentthe end 4 of the housing 2. However, rotation of the sleeve 19 isretarded by frictional engagement of an inturned flange 21 on the outerend of the sleeve with a large friction bearing 22 contained in a recess23 in the housing end wall 4 surrounding the screw shaft 8, for apurpose to be fully described hereafter.

interposed between the inturned flange 21 and a thrust washer 28adjacent the outer end of the clutch element 18 are a plurality ofneedle thrust bearings 24. Accordingly when the nut 11 is rotated in aclutch disengaging direction causing linear outward movement of thescrew shaft 8 against a compression load, the nut 11 and clutch element18 are free to rotate relative to the sleeve, and any thrust loadsacting on the screw shaft 8 in opposition to such linear outwardmovement are taken by the needle bearings 24 for high efficiencyoperation.

The direction-sensitive clutch 15 prevents back driving or overhaulingof the actuator 1 by the applied load in the opposite direction, sincelinear inward movement of the screw shaft rotates the nut 11 and clutchelement 18 in the reverse direction causing the clutch rollers 16 tomove outwardly into wedging engagement between the cam surfaces 17 onthe clutch element and the inner periphery of the sleeve 19. Helicalsprings 25 disposed in recesses 26 in the clutch element 18 assist inurging the clutch rollers 16 outwardly along the cam surfaces formaintaining a driving connection between the sleeve 19 and clutchelement 18 during rotation of the clutch element in the clutch engagingdirection.

With a driving connection between the sleeve 19 and clutch element 18,there is a resistance to rotation of the clutch element 18 which resistslinear inward movement of the screw shaft 8 because of the frictionalcontact of the inturned flange 21 on the sleeve 19 with the largefriction bearing 22. The friction bearing 22 may be made large enough toabsorb all of the energy due to back driving or overhauling by the load,since the energy absorption capability of the large friction bearing isdirectly proportional to the applied load in the overhauling direction.Thus, linear inward movement of the screw shaft 8 may be prevented bythe one-way clutch l and friction bearing 22 except when a net positiveinput torque is applied to the nut 11 by the input shaft 12 for positivecontrol of the screw shaft 8 during linear inward movements as well.

If the prevailing load acting on the actuator is in tension rather thancompression, the actuator connections may be reversed or the one-wayclutch 15, sleeve 19, and friction bearing 22 may be located at theother end of the housing 2 as shown in FIG. 3 to eliminate any backdriving tendency in the linear outward direction with no decrease inefficiency during linear inward movement.

Moreover, bi-directional braking may also be provided so that mass loador overhauling load applications requiring over-center motion may beprevented from back driving in either direction by providing axialfreedom of the drive gear 14 and placing a large friction bearing 27 atthe other end of the housing 2 as well as shown in FIG. 4 for frictionalengagement by the outer end of the drive gear 14' if the load shifts forexample from a compression load to a tension load. Otherwise, thedetails of construction and operation of the linear actuator of the FIG.4 embodiment are substantially identical to the linear actuatorspreviously described, and accordingly the same reference numeralsfollowed by a prime symbol are used to designate like parts.

From the foregoing, it will now be apparent that the linear actuators ofthe present invention effectively eliminate any back driving tendency ofthe load in one or both directions while providing high efficiencyduring movement of the actuator against the opposing load. Theresistance to movement of the actuator in the load-aiding direction isdirectly proportional to the applied load, whereby a net positive inputtorque may be required to move the actuator in the load-aidingdirection. In each of the embodiments disclosed, the nut is rotatableand the screw is fixed against rotation. However, it will be apparentthat the same principles are applicable where either the nut or thescrew is the rotating member.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

l. A linear actuator comprising a housing, a screw shaft extending fromsaid housing, a nut having threaded engagement with said screw shaft,means for rotating said nut relative to said screw shaft for effectinglinear movement of said screw shaft, one-way clutch means attached toone end of said nut for rotation therewith, and friction meansengageable by said one-way clutch means for resisting rotation of saidnut in one direction, said one-way clutch means being freely rotatablewith respect to said friction means in the reverse direction.

2. The actuator of claim 1 wherein said friction means comprises arotatable sleeve surrounding said one-way clutch means and driventhereby during rotation of said nut in one direction but not in theother direction, and a friction bearing fixed with respect to saidhousing engageable by said sleeve to provide resistance to turningofsaid sleeve.

3. The actuator of claim 2 wherein said friction bearing is fixed withinsaid housing adjacent one end thereof, and said rotatable sleeve has aninturned flange in contact with said friction bearing.

4. The actuator of claim 3 further comprising antifriction bearingsinterposed between said inturned flange and clutch means to permit freerotation of said clutch means relative to said sleeve in thenon-engaging direction of said clutch means.

5. The actuator of claim 3 wherein said clutch means drivingly engagessaid sleeve during rotation in a direction causing linear inwardmovement of said screw shaft for providing resistance to turning of saidscrew shaft when an applied load acting on the end of said screw shafturges said screw shaft inwardly, said friction bearing being at the endof said housing furthest from the applied load.

6. The actuator of claim 3.w herein said clutch means drivingly engagessaid sleeve during rotation in a direction causing linear outwardmovement of said screw shaft for providing resistance to turning of saidscrew shaft when an applied load acting on the end of said screw shafturges said screw shaft outwardly, said friction bearing being at the endof said housing closest to the applied load.

7. A linear actuator comprising a housing, a screw shaft extending fromsaid housing, a nut having threaded engagement with said screw shaft,means for rotating said nut relative to said screw shaft for effectinglinear movement of said screw shaft, one-way clutch means attached toone end of said nut for rotation therewith, and friction meansengageable by said one-way clutch means for resisting rotation of saidnut in one direction, said one-way clutch means being freely rotatablewith respectto said friction means in the reverse direction, saidfriction means comprising a rotatable sleeve surrounding said one-wayclutch means and driven thereby during rotation of said nut in onedirection but not in the other direction, and a friction bearing fixedwith respect to said housing engageable by said sleeve to provideresistance to turning of said sleeve, said friction bearing being fixedwithin said housing adjacent one end thereof, and said rotatable sleevehaving an inturned flange in contact with said friction bearing, and anadditional friction bearing adjacent the other end of said nut forengagement thereby upon a reversal in the direction of the applied loadto provide bidirectional braking.

8. The actuator of claim 7 wherein said means for rotating said nutcomprises a rotary input shaft, and gearing on said input shaft and nutfor driving said nut during rotation of said input shaft, said gearingon said nut being engageable with said additional friction bearing upona reversal in the direction of the applied load as aforesaid.

9. The actuator of claim 7 further comprising antifriction bearingsinterposed between said inturned flange and clutch means to permit freerotation of said clutch means relative to said sleeve in thenon-engaging direction of said clutch means.

10. The actuator of claim 7 wherein said friction bearing provides aresistance to turning of said sleeve directly proportional to an appliedload acting on the end of said screw shaft urging said inturned flangeinto frictional engagement with said friction bearing.

l l l 1

1. A linear actuator comprising a housing, a screw shaft extending fromsaid housing, a nut having threaded engagement with said screw shaft,means for rotating said nut relative to said screw shaft for effectinglinear movement of said screw shaft, one-way clutch means attached toone end of said nut for rotation therewith, and friction meansengageable by said one-way clutch means for resisting rotation of saidnut in one direction, said one-way clutch means being freely rotatablewith respect to said friction means in the reverse direction.
 2. Theactuator of claim 1 wherein said friction means comprises a rotatablesleeve surrounding said one-way clutch means and driven thereby duringrotation of said nut in one direction but not in the other direction,and a friction bearing fixed with respect to said housing engageable bysaid sleeve to provide resistance to turning of said sleeve.
 3. Theactuator of claim 2 wherein said friction bearing is fixed within saidhousing adjacent one end thereof, and said rotatable sleeve has aninturned flange in contact with said friction bearing.
 4. The actuatorof claim 3 further comprising anti-friction bearings interposed betweensaid inturned flange and clutch means to permit free rotation of saidclutch means relative to said sleeve in the non-engaging direction ofsaid clutch means.
 5. The actuator of claim 3 wherein said clutch meansdrivingly engages said sleeve during rotation in a direction causinglinear inward movement of said screw shaft for providing resistance toturning of said screw shaft when an applied load acting on the end ofsaid screw shaft urges said screw shaft inwardly, said friction bearingbeing at the end of said housing furthest from the applied load.
 6. Theactuator of claim 3 whErein said clutch means drivingly engages saidsleeve during rotation in a direction causing linear outward movement ofsaid screw shaft for providing resistance to turning of said screw shaftwhen an applied load acting on the end of said screw shaft urges saidscrew shaft outwardly, said friction bearing being at the end of saidhousing closest to the applied load.
 7. A linear actuator comprising ahousing, a screw shaft extending from said housing, a nut havingthreaded engagement with said screw shaft, means for rotating said nutrelative to said screw shaft for effecting linear movement of said screwshaft, one-way clutch means attached to one end of said nut for rotationtherewith, and friction means engageable by said one-way clutch meansfor resisting rotation of said nut in one direction, said one-way clutchmeans being freely rotatable with respect to said friction means in thereverse direction, said friction means comprising a rotatable sleevesurrounding said one-way clutch means and driven thereby during rotationof said nut in one direction but not in the other direction, and afriction bearing fixed with respect to said housing engageable by saidsleeve to provide resistance to turning of said sleeve, said frictionbearing being fixed within said housing adjacent one end thereof, andsaid rotatable sleeve having an inturned flange in contact with saidfriction bearing, and an additional friction bearing adjacent the otherend of said nut for engagement thereby upon a reversal in the directionof the applied load to provide bidirectional braking.
 8. The actuator ofclaim 7 wherein said means for rotating said nut comprises a rotaryinput shaft, and gearing on said input shaft and nut for driving saidnut during rotation of said input shaft, said gearing on said nut beingengageable with said additional friction bearing upon a reversal in thedirection of the applied load as aforesaid.
 9. The actuator of claim 7further comprising anti-friction bearings interposed between saidinturned flange and clutch means to permit free rotation of said clutchmeans relative to said sleeve in the non-engaging direction of saidclutch means.
 10. The actuator of claim 7 wherein said friction bearingprovides a resistance to turning of said sleeve directly proportional toan applied load acting on the end of said screw shaft urging saidinturned flange into frictional engagement with said friction bearing.